Copolymers of 2-vinylpyridine and styrene are known for use as a pH-sensitive coating for orally administrable drugs, nutrients, and medicaments, particularly for the ruminants (U.S. Pats. Nos. 4,177,255, 4,181,708, 4,181,709, 4,181,710). These polymers when prepared by emulsion polymerization are generally precipitated by drowning into sodium chloride solution. Our experience has shown that the filtration and washing of the cake is slow and that the wet cake has % solids of about 30-35%. The low solids and the face that such cake is thixotropic makes the drying process difficult. Furthermore, solubility problems have been experiencd during the coating process which were traced to excessive NaCl left from the wet cake.
A typical procedure for isolating copolymer of 2-vinylpyridine and styrene calls for drowning the reaction emulsion into a sodium chloride/water solution. This affords a product that is small in particle size and filters and washes slowly. The wet cake produced from such work-up generally has about 30 to 35% solids. A method that improves the filtration, washing, and % solids of the wet cakes also saves time in the subsequent drying.
A procedure is disclosed in U.S. Pat. No. 2,830,975 whereby a polymer s coagulated with an acidic material, such as sulfuric acid, hydrochloric acid, acetic acid, or the like. A highly ionizing acid is preferred. One method of effecting coagulation is to pass separate streams of the latex and coagulant to a coagulating vessel. Another method comprises blending separate streams of the latex and coagulant just prior to the entrance of the combined streams into the coagulating vessel. The materials are agitated during coagulation and the pH of the serum is preferably maintained below a pH of about 4.